The present invention concerns an electric resistor heating element according to the preamble of claim 1. Such resistor heating elements are used in many sectors, e.g., as floor radiation heating in the building industry. The resistor heating elements traditionally used where the heat is generated by so-called heating filaments or heater foils have the disadvantage of being sensitive to mechanical stress and of requiring a specialist for precise installation. In the document U.S. Pat. No. 4,801,784, a self-regulating heating element for the cable accessories and pipe protection industry is described which works with flat electrodes and a resistive layer arranged between the flat electrodes. In such a heating element, the flat electrodes are connected to the power supply lines, with rivets for instance. Thus, compression must be applied when making the connections, at which occasion a contact between the flat electrodes and hence a short circuit can occur.
Further, from the document DE-A1-2,856,178 an electric heater blanket is known where the heating conductors are laminated or coated onto a base film. For a connection of these heating conductors with the heating conductors of neighboring heater blankets, connection zones are provided where the bare heating conductors are exposed and can be connected by a galvanic process using solder or by mechanical methods using rivets. With such a structure, there is no risk of a short circuit since flat electrodes which could come in contact during riveting are not intended to be used. However, in the production of a heater blanket having certain dimensions, it may become necessary to connect a plurality of heater blankets.
For the use of a resistor heating element as a floor radiation heating, for instance, a uniform heat transfer across the surface on one hand and simple, durable installation and electrical connections on the other hand are important. Moreover, it must be possible to flexibly design the dimensions of the resistor heating element in order to accommodate the size of the surface to be heated.
It is the aim of the present invention, therefore, to provide a resistor heating element where without the risk of a short circuit or of injury to the resistor heating element, the electrical connections can be made in a simple way and so that they will at once resist mechanical stresses. It should further be possible to manufacture the resistor heating element in a continuous fashion, flexibly select its size, manipulate it in a simple way, and use it even in wet surroundings.
According to the invention, this aim is attained by a resistor heating element having the features of the characterizing part of claim 1. Advantageous further embodiments of the invention are described in the dependent claims. Flat electrodes in the sense of this invention is the term used for electroconductive layers adjacent to the resistive layer which are used for current feed.
The resistor heating element according to the invention, also designated as a resistor sandwich, offers predefined contact points based on recesses in the flat electrodes where one flat electrode at a time can readily be connected with the current feeder line. The contacts can be made by using high clamping pressures. With a resistor heating element having two flat electrodes, the tool is then applied in such a way that on one hand it penetrates into the recess of one flat electrode and on the other hand clasps the resistive layer, the other flat electrode, and the current feeder device or contact element. Because of the recess, a contact between the flat electrodes cannot arise even at high compression, thus avoiding a breakdown or arc-over of voltage.
When making a force or form-locking connection between the current feeder lead and the flat electrode in the resistor heating element according to the invention, it is also possible to use contact components connecting in depth with the flat electrodes. In this case clamps can be used which at predetermined points penetrate from above and below into the resistor heating element via electroconductive contact lugs or teeth. One of the contact lugs is introduced from one side of the resistor heating element into the recess of the first flat electrode, penetrates the resistive layer, and is in contact with the second flat electrode. The second contact lug makes contact with the second flat electrode from the other side. The two contact lugs in turn are electrically connected with a current feeder line, for instance with the phase conductor. Such an in-depth electrical contact with a resistor heating element can only be made with a resistor heating element according to the invention. In the case of traditional resistor heating elements, such a way of making electrical contacts would short-circuit the flat electrodes and damage the resistor heating element. Beyond the precise connection of exactly one flat electrode, the way of making contacts according to the invention also has the advantage that the form-locking connection between the flat electrode and the current feeder can withstand tensile and tangential stresses.
A seal, for instance in the form of a silicone lip, can be provided around each contact component. In the resistor heating element according to the invention, the contact component can be applied with the pressure required for sealing. Possible uses in wet surroundings are thus opened up.
The resistor heating element according to the invention can readily be produced by traditional lamination operations, and because of the small risk of a short circuit encountered when making the electrical contacts, can also be connected and installed by workers (such as construction workers) having little electrotechnical training.
By suitable arrangement of the recesses in the border zones of the electroconductive layers, each single layer of the two or more layers can be contacted selectively. Thus, a ground wire, a neutral conductor and a layer connected to the phase conductor can be arranged within the resistor heating element. Each of these layers can be electrically connected individually in depth without short-circuiting the electroconductive layers. None of the three layers will come into contact with another layer, even when making the electrical connections while using high compression, so that a short circuit is effectively prevented.
According to claim 4, several groups of recesses can be provided along the borders of each of the electroconductive layers in the resistor heating element, each individual layer having at least one recess. The distances between the groups of recesses are preferably uniform.
Thus, in this embodiment several contact points are available at the border of the resistor heating element. The number of recesses to be provided per group depends on the number of electroconductive layers present in the resistor heating element. The number of recesses per group preferably is one less than the number of layers. In view of the large number of contact points, a decision can be made on the spot when installing the resistor heating element, as to which of the contact points are nearest to the current source and hence should be connected to it.
In the embodiment according to claim 5, additional contact possibilities are provided across the surface, apart from those existing in the border zone of the resistor heating element. When cutting the resistor heating element, and with the cut passing through the additional recesses provided across the surface, one can use these recesses as border contact points after splitting the resistor heating element. In this embodiment, therefore, the resistor heating element can be cut up on the spot to parts having the desired size, while always several possibilities will be available along the border of the resistor heating element for making electrical connections with the individual electroconductive layers.
The spatial separation of the projections of the individual recesses yields enhanced safety in avoiding the contact between the electroconductive layers or contact lugs of the current feeder leads. The contacting component, for instance a clamp with contact lugs, which as a rule has dimensions smaller than the recess, need not be inserted exactly into the center of the recess of one of the electroconductive layers in this preferred embodiment but can also engage close to the edge of the recess so long as it meets the condition of claim 2. This additional safety mechanism considerably facilitates the making of electrical connections at the resistor heating element, and no precision tools are needed for it.
The embodiment according to claim 6 has the advantage that straight cuts can be performed along one of the longitudinal or transverse lines along which the additional recesses are arranged when the resistor heating element is cut down to the desired size.
Furthermore, according to claim 7 or 8, a short circuit and other damage, for instance by a disruptive discharge of the voltage, is avoided at points where a short circuit might occur, for instance in the zone where forces act during the making of electrical connections, by providing free or nonconducting zones. A filler material that might be present can be so selected that it is insulating and at the same time has reinforcing or stiffening properties. This can serve to provide additional stability to the resistor heating element in individual zones, and to insulate the electroconductive layers from each other.
The recesses provided in the border zone of the resistive mass provide additional safety since it is in this zone that electrical connections are made and forces are applied. The mosaic-like array of such zones along lines in the longitudinal and transverse direction of the resistor heating element which preferably coincide with the lines along which the additional recesses across the surface of the electroconductive layers are arranged, facilitates the splitting of the resistor heating element into smaller pieces since the lines serve as the cutting edges. Particularly in the presence of filler materials having stiffening or reinforcing properties, therefore, injury to the resistor heating element arising from a compression of the resistive layer along the cutting edge can thus be avoided. Moreover, the insulating properties of the filler material can also counteract a short circuit, particularly at the points of the recesses where the electrical connections are made.
Openings in the electroconductive layers according to claim 9 or 10 which can for instance be present in the form of circular holes allow the resistor heating element to be fixed at the wall or on the floor with traditional fasteners such as nails or screws. The openings then prevent a short circuit that could be produced by the nail or screw.
The filler material which preferably has reinforcing or stiffening properties and can serve as an insulation can also function as an additional fixation in the region of the openings. By passing the screw or nail through the resistive layer which at this point is provided with filler material, a radial slip of the screw inside the opening, for instance because of the resistor heating element""s own weight when fixed at a wall, can be prevented by the filler material.
In a resistive layer comprising a support material which according to claim 11 is coated with the resistive mass, the elasticity or plasticity of the resistive layer can be adjusted by appropriate selection of the support material. Moreover, even the resistance value of the resistive layer can be adjusted in an ideal manner when such a structure is present. The more highly porous the support material selected, the larger will be the amount of resistive mass that can be taken up by it. Moreover, the support material can be present as a continuous layer where only those regions that should be free of resistive mass are bypassed when coating the layer with resistive mass. The preparation of the resistive layer which for instance can occur by offset printing is simple and admits a precise layout of regions with and without resistive mass.
An electroconductive polymer is readily applied to a support material; at the same time high electric heating outputs can be achieved with such a resistive mass. Moreover, the electroconductive polymer is flexible so that even a mechanical stress, for instance when the resistor heating element is rolled up, will not lead to injury of the resistive mass and thus to undesirable ruptures in electric conduction within the resistor heating element.
In the following the invention will be explained with reference to the appended drawings showing:
In FIG. 1a a perspective view of a resistor heating element according to the invention with two flat electrodes;
In FIG. 1b a top view of the resistor heating element of FIG. 1a according to the invention;
In FIG. 2 a perspective cutaway of an embodiment of the resistor heating element according to the invention with two flat electrodes and an additional electroconductive layer;
In FIG. 3 a partial section through a resistor heating element according to FIG. 2 with contacting component;
In FIG. 4 a top view of a resistor heating element according to the invention with two flat electrodes, an additional electroconductive layer and several recesses across the surface.